1. Field of the Invention
The present invention relates to a conjugated diene random copolymer having an alkoxysilane unit. More particularly, the present invention relates to a conjugated diene random copolymer which is prepared by subjecting a conjugated diene monomer, an aromatic vinyl monomer and an alkoxysilane monomer having a specific structure to emulsion polymerization, wherein the copolymer contains an alkoxysilane unit in the backbone thereof and is thus enhanced in the degree of dispersion and affinity to a reinforcing material such as carbon black or silica, and is useful as a rubber material for tires having superior mechanical and dynamic properties.
2. Description of the Related Art
With the recent increasing interest in development of eco-friendly and energy-saving tires having high functionality, thorough research is ongoing to develop highly functional rubber adapted therefor. In order to develop tires having high functionality, it is essential to develop rubber which satisfies dynamic properties including high wet traction and low rolling resistance, which may directly affect fuel efficiency.
Typical tire rubber includes conjugated diene polymers such as styrene-butadiene rubber (hereinafter referred to as “SBR”) or butadiene rubber (hereinafter referred to as “BR”), which may be prepared using solution polymerization or emulsion polymerization.
In solution polymerization (SSBR), rubber is typically prepared in the presence of an organic solvent using organic lithium as an initiator. Upon rubber preparation using solution polymerization, it is possible to adjust the micro molecular structure, including the vinyl structure of conjugated diene, the block ratio of styrene molecule, etc., and also it is easy to modify the physical properties of polymers using a functional to initiator or a terminal modifier. Accordingly, conjugated diene polymers having a silane functional group introduced to the terminal thereof are mainly synthesized using solution polymerization [U.S. Pat. Nos. 5,508,333 and 6,133,388, and US Patent Application Nos. 2010-0152369 and 2011-0207879]
In emulsion polymerization (ESBR), rubber is typically prepared using a radical polymerization initiator. Upon rubber preparation using emulsion polymerization, it is not easy to adjust the molecular structure and also it is difficult to modify physical properties of the polymer by the introduction of the functional group.
Conventional techniques for synthesizing conjugated diene-based polymers having enhanced compatibility with inorganic materials such as carbon black or silica using emulsion polymerization are as follows.
U.S. Pat. Nos. 3,575,913 and 3,563,946 disclose techniques for preparing styrene-butadiene or styrene-butadiene-acrylate copolymers by emulsion polymerization using potassium persulfate or azobisisobutyronitrile as a radical polymerization initiator.
U.S. Pat. No. 4,064,081 discloses a technique for preparing a butadiene-styrene-itaconic acid copolymer by emulsion polymerization using potassium persulfate as a radical polymerization initiator.
U.S. Pat. Nos. 5,274,027 and 5,302,655 disclose techniques for preparing styrene-butadiene-acrylate copolymers by emulsion polymerization of acrylate-based monomers such as methyl methacrylic acid and itaconic acid using ammonium persulate as a radical polymerization initiator.
As mentioned above, adjusting the molecular structure of the conjugated diene polymers resulting from emulsion polymerization is not easy, thus making it difficult to control the properties of polymers by the use of the functional monomers. For this reason, almost no attempts have been made to prepare conjugated diene random copolymers from alkoxysilane-substituted monomers.